In recent years, fuel cell systems which employ, as an energy source, a fuel cell that generates electric power through electrochemical reaction between a fuel gas (an anode gas) and an oxidant gas (a cathode gas) have been increasingly attracting attention. One known example of fuel cells used in such fuel cell systems has a fuel cell stack in which a plurality of unit cells are stacked, with the fuel cell stack being sandwiched by end plates arranged on both ends in the cell-stacking direction of the fuel cell stack.
Some of these fuel cell systems may comprise a fuel gas circulation system (circulation passage) for returning a fuel off-gas (hydrogen off-gas) discharged from the fuel cell stack and resupplying it to the fuel cell stack in order to efficiently use a fuel gas such as hydrogen gas. For example, the applicant has proposed a fuel cell system in which, for the purpose of preventing water contained in the fuel off-gas from freezing at a point of merger between the fuel off-gas and a newly-supplied fuel gas and allowing easy arrangement of auxiliary machines along a fuel off-gas circulation passage, the point of merger and a part of the fuel off-gas circulation passage are provided in end plates (see Patent Document 1, etc.).